Press molding die and manufacturing method of same

ABSTRACT

A press molding die capable of preventing a workpiece from moving is provided. The press molding die includes a punch for pressing a workpiece; a molding die having a molding surface on which the workpiece is placed and a concave portion which is formed on the molding surface and which has a shape corresponding to the punch; a pad for pressing a part of the workpiece placed on the molding surface and which is on the periphery of the concave portion; and a micro-rough layer which is formed by performing a particulate coating process on at least one of a portion of the pad, for pressing the workpiece, and a portion of the molding surface, corresponding to the portion of the pad. Preferably, the height of roughness of the micro-rough layer is 0.01 to 0.06 mm, and the particulate coating process is performed using a silicofluoric chrome plating solution.

INCORPORATION BY REFERENCE

[0001] The disclosure of Japanese Patent Application No. 2003-097962filed on Apr. 1, 2003, including the specification, drawings andabstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to a press molding die capable ofpreventing a workpiece from moving during press molding, and amanufacturing method of same.

[0004] 2. Description of the Related Art

[0005] In order to press a platy workpiece into shapes, initially, theworkpiece is placed on a molding surface of a molding die having apredetermined-shaped concave portion. On the periphery of the concaveportion, the workpiece is pressed to the molding die by a pad and isfixed. Then, the workpiece is plastically deformed by being pressed by apunch having a shape corresponding to the concave portion. In such pressmolding, a problem occurs that the workpiece moves into the concaveportion, that is, so-called displacement of the workpiece is caused. Thedisplacement of the workpiece affects the accuracy of a press moldedproduct, the quality of a surface of the press molded product, and thelike. In addition, due to such a problem useful lives of the molding dieand the punch are shortened, and the cost of maintenance of the moldingdie and the punch increases.

[0006] An example of methods for preventing the workpiece from moving isto increase the pressing force of the pad during press molding. However,since the pressing force of the pad acts in the direction perpendicularto the direction in which the workpiece moves, it is necessary to applya tremendous amount of pressing force in order to prevent the workpiecefrom moving. Also, it is impossible to prevent the workpiece from movingsubstantially completely. It is also possible to prevent the workpiecefrom moving by precisely controlling the distance between the moldingdie and the pad. However, such control requires a complicatedconfiguration of the die and skills in adjustment, thereby increasingthe cost of manufacturing the die.

[0007] As related art, Japanese Patent Laid-Open Publication No.3-268808 discloses a known metalworking tool for suppressing occurrenceof a weld marks which are likely to occur during cold work and presswork of metal, and for preventing a slip which occurs due to lubricatingoil used for preventing occurrence of the weld marks. The metalworkingtool is a plastic forming tool and a plurality of small dents is formedon the smooth surface of the metalworking tool. Each of the dents has adiameter of 5 to 50 μm, and a depth of 0.5 to 5 μm. The total area ofthe dents accounts for 5 to 50% of the surface area of the tool beforethe dents are formed.

SUMMARY OF THE INVENTION

[0008] According to an aspect of the invention, a press molding die isprovided. The press molding die includes a punch which presses aworkpiece; a molding die having a molding surface on which the workpieceis placed and a concave portion which is formed on the molding surfaceand which has a shape corresponding to the punch; a pad which presses aportion that is a part of the workpiece placed on the molding surfaceand that is on the periphery of the concave portion; and a layer havingmicro-roughness (hereinafter, referred to as a “micro-rough layer”)which is formed by performing a particulate coating process on at leastone of a portion of the pad, for pressing the workpiece, and a portionof the molding surface, corresponding to the portion of the pad, forpressing the workpiece.

[0009] According to another aspect of the invention, a method formanufacturing a press molding die is provided. The manufacturing methodincludes a step for forming a punch which presses a workpiece; a stepfor forming a molding die having a molding surface on which theworkpiece is placed and a concave portion which is formed on the moldingsurface and which has a shape corresponding to the punch; a step forforming a pad which presses a portion that is a part of the workpieceplaced on the molding surface and that is on the periphery of theconcave portion; and a step for forming a micro-rough layer byperforming a particulate coating process on at least one of a portion ofthe pad, for pressing the workpiece, and a portion of the moldingsurface, corresponding to the portion of the pad for pressing theworkpiece.

[0010] According to the press molding die and the manufacturing methodof same, by forming the micro-rough layer on at least one of the portionof the pad and the portion of the molding die, which are on theperiphery of the concave portion, the roughness of the micro-rough layerdeforms the workpiece such that the deformation prevents the workpiecefrom moving. As a result, it is possible to prevent the workpiece frommoving into the concave portion.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The above-mentioned embodiment and other embodiments, objects,features, advantages, technical and industrial significance of thisinvention will be better understood by reading the following detaileddescription of the exemplary embodiments of the invention, whenconsidered in connection with the accompanying drawings in which:

[0012]FIG. 1 a cross sectional view of a press molding die according tothe invention, during press molding;

[0013]FIG. 2 is a cross sectional view showing an example of amicro-rough layer;

[0014]FIG. 3A is a top view showing an example of a concave portion ofthe molding die and grooves formed on the periphery of the concaveportion;

[0015]FIG. 3B is a top view showing another example of a concave portionof the molding die and grooves formed on the periphery of the concaveportion;

[0016]FIG. 4 is a microscope photograph of a micro-rough layer formed ina first embodiment;

[0017]FIG. 5 is a pattern diagram of the microscope photograph shown inFIG. 4;

[0018]FIG. 6 is a microscope photograph of a micro-rough layer formed ina second embodiment; and

[0019]FIG. 7 is a pattern diagram of the microscope photograph shown inFIG. 6.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0020] In the following description, the present invention will bedescribed in more detail in terms of exemplary embodiments.

[0021]FIG. 1 is a view schematically showing a press molding dieaccording to the invention. The press molding die includes a molding die1, a pad 2, and a punch 3, and is used for pressing a platy workpiece 4into shapes. In the press molding die, a concave portion 5 having ashape corresponding to the punch 3 is formed on a molding surface of themolding die 1. The workpiece 4 placed on the molding surface is pressedto the molding die 1 by the pad 2 and is fixed, on the periphery of theconcave portion 5. In this case, the press molding die according to theinvention is characterized in that a micro-rough layer 6 is formed byperforming a particulate coating process on at least one of a portion ofthe pad 2, for pressing the workpiece 4, and a portion of the moldingsurface, corresponding to the portion of the pad 2, for pressing theworkpiece 4.

[0022] In the press molding die, when the workpiece 4 is sandwichedbetween the molding die 1 and the pad 2 and is pressed by the pad 2, theroughness of the micro-rough layer 6 deforms the workpiece 4 using thepressing force of the pad 2. The deformation acts as resistance in thedirection perpendicular to the direction in which the workpiece 4 moves.In the press molding die according to the invention, the workpiece 4contacts the molding die 1 only at the convex portions of themicro-rough layer 6. Therefore, in the case where the micro-rough layer6 is formed, the pressing force applied to the workpiece 4 per unit areais larger than that in the case where the micro-rough layer 6 is notformed, even the pressing force applied by the pad 2 is the same. As aresult, it is possible to effectively prevent the workpiece 4 frommoving.

[0023] It is preferable to set the height of the roughness of themicro-rough layer 6 to 0.01 to 0.06 mm. If the height of the roughnessof the micro-rough layer 6 is smaller than 0.01 mm, the effect ofpreventing the workpiece 4 from moving using the micro-rough layer 6cannot be obtained effectively. On the other hand, if the height of theroughness of the micro-rough layer 6 exceeds 0.06 mm, there occurstransfer marks which are sufficiently large to be visually observed evencoating is applied to the molding surface after the workpiece is molded,which degrades the appearance quality of the molded product.

[0024] The micro-rough layer 6 is formed by performing the particulatecoating process. In the particulate coating process, the size of aparticle of the metal having high hardness is increased on the platingsurface. The plating process needs to be performed at an appropriatetemperature of the plating solution, an appropriate current density andthe like. Also, the plating process is preferably performed using asilicofluoric chrome plating solution.

[0025] The silicofluoric chrome plating solution preferably contains 200to 300 g of chromic anhydride, 1 to 8 g of sodium silicofluoride, and0.5 to 1.5 g of sulfuric acid per liter. The particulate coating processis preferably performed using the plating solution, in the condition inwhich the temperature of the plating solution is 40 to 50° C., thecurrent density is 100 to 150 A/dm², and the plating time is 3 to 10minutes. The thus obtained micro-rough layer 6 has physical propertiessuch as a thickness of 10 to 40 μm, a hardness of 1000 to 1100 HV, aparticle diameter of 10 to 30 μm, and surface roughness of 10 to 30μmRy. Also, the adhesion of the micro-rough layer 6 to the press moldingdie is high. Accordingly, it is possible to sufficiently satisfy therequirements on the micro-rough layer 6 which is formed on the pressmolding die.

[0026] The particulate coating process for forming the micro-rough layer6 can be performed in the same process as a common plating process.Initially, a surface of the press molding die, on which the particulatecoating process is performed, is degreased, and another surface, onwhich the particulate coating process is not performed, is masked. Then,the press molding die is set on a jig, and an anode and a cathode areset. Then, the press molding die is immersed, for example, in thesilicofluoric chrome plating solution having the above-mentionedcomposition. Electric power is supplied for a predetermined period, thepress molding die is taken out from the silicofluoric chrome platingsolution, is washed, the jig is removed, and the press molding die isdried. Thus, the micro-rough layer 6 is formed by the particulatecoating process.

[0027] The micro-rough layer 6 may be formed of a plurality of platedlayers, as shown in FIG. 2. In the example shown in FIG. 2, themicro-rough layer 6 is formed of a lower side plated layer 71 having asmooth surface, and an upper side plated layer 72 which is formed by theparticulate coating process and which has roughness. In the case wherethe micro-rough layer 6 is formed of two plated layers, durability ofthe press molding die and the micro-rough layer 6 can be enhanced,compared with the case where the micro-rough layer 6 is formed only bythe particulate coating process.

[0028] On the molding surface of the press molding die, grooves whichare formed by common machining may be formed, in addition to themicro-rough layer 6. A plurality of grooves which are parallel to eachother, and another plurality of grooves which are parallel to each otherare formed such that the plurality of grooves and the other plurality ofgrooves extend in different directions. The grooves formed in thedirection parallel to the direction in which the workpiece 4 moves havelow degree of resistance to the movement of the workpiece 4. Therefore,it is preferable to form the grooves in the direction substantiallyperpendicular to the direction in which the workpiece 4 moves.

[0029] Concrete examples of the grooves are shown in FIG. 3 which is thetop view of the molding die 1, at the center of which is the concaveportion 5. In the example shown in FIG. 3A, a plurality of verticalgrooves 81 and another plurality of horizontal grooves 82 which areperpendicular to each other are formed on the molding surface of themolding die 1. The distance between the grooves is, for example, 2 mm.In the example shown in FIG. 3B, grooves 83 each of which has a shapesimilar to that of the periphery of the concave portion 5. The grooves83 are formed in a loop shape so as to surround the concave portion 5.The direction in which the workpiece 4 moves is the direction radiatingfrom the concave portion 5. Therefore, the grooves 83 are formed in thedirection perpendicular to all the directions in which the workpiece 4moves, and the effect of preventing the workpiece 4 from moving isparticularly high. The grooves can be formed by shot blasting, ceramicspraying, pattern plating, laser spraying, or the like.

[0030] In the press molding using the press molding die according to theinvention, initially, the workpiece 4 is placed on the molding die 1such that the rear surface of the workpiece 4 faces the molding surfaceof the molding die 1. Then, the workpiece 4 is pressed to the pressmolding die by the pad 2, and is fixed. The workpiece 4 is then pressedby the punch 3 so as to be plastically deformed. In this case, theworkpiece 4 contacts only the convex portions of the micro-rough layer 6of the press molding die. Therefore, the pressing force applied to theworkpiece 4 per unit area is considerably large, compared with the casewhere the micro-rough layer 6 is not formed. As the punch 3 is moveddownward, the force for moving the workpiece 4 into the concave portion5 is generated. At this time, the roughness of the micro-rough layerdeforms the workpiece such that the deformation prevents the workpiecefrom moving. The micro-rough layer 6 generates transfer marks on therear surface of the workpiece 4. However, since the micro-rough layer 6does not affect the front surface of the workpiece 4, the appearancequality of the workpiece 4 is not affected.

[0031] A micro-rough layer was formed on a surface of a molding die bythe particulate coating process using a plating solution and platingconditions shown in the following table. A microscope photograph of theformed micro-rough layer was taken. FIG. 4 shows the microscopephotograph of the micro-rough layer formed in the first embodiment. FIG.5 is a pattern diagram of the microscope photograph shown in FIG. 4.FIG. 6 shows the microscope photograph of the micro-rough layer formedin the second embodiment. FIG. 7 is a pattern diagram of the microscopephotograph shown in FIG. 6. The diameter of the particle of the formedmicro-rough layer was decided, and the thickness of the plating wasmeasured by an electromagnetic thicknessmeter. Then, press molding wasperformed using both of the molding dies, and movement of the workpieceduring press molding and the surface properties of the workpiece afterpress molding were evaluated. Table 1 shows the result of theevaluation. TABLE 1 First Second embodiment embodiment Plating solutioncomposition Chromic acid concentration 234.3 g/L  249.9 g/L  Sulfuricacid concentration 0.9 g/L 1.0 g/L Sodium silicofluoride concentration6.3 g/L 6.8 g/L Plating conditions Solution temperature 45° C. 45° C.Current density 120 A/dm² 150 A/dm² Plating time 5 min. 5 min.Micro-rough layer evaluation Particle diameter 20 μm 25 μm (average)(average) Plating thickness approximately approximately 25 μm 30 μmPress molding evaluation Workpiece movement None None Workpiece surfaceproperties Good Good

[0032] According to the invention, a micro-rough layer is formed on amolding surface of a press molding die, at a portion to which aworkpiece is pressed by a pad and is fixed. With this arrangement, it ispossible to prevent the workpiece from moving into a concave portion,that is, it is possible to prevent so-called displacement of theworkpiece, without accurately controlling the conditions of pressmolding. Since the micro-rough layer is formed by the particulatecoating process, it is possible to obtain a press molding die with asimple configuration, and to manufacture the press molding die at lowcost.

[0033] While the invention has been described with reference toexemplary embodiments thereof, it is to be understood that the inventionis not limited to the exemplary embodiments or constructions. To thecontrary, the invention is intended to cover various modifications andequivalent arrangements. In addition, while the various elements of theexemplary embodiments are shown in various combinations andconfigurations, which are exemplary, other embodiments andconfigurations, including more, less or only a single element, are alsowithin the spirit and scope of the invention.

What is claimed is:
 1. A press molding die, comprising: a punch whichpresses a workpiece; a molding die having a molding surface on which theworkpiece is placed and a concave portion which is formed on the moldingsurface and which has a shape corresponding to the punch; a pad whichpresses a portion that is a part of the workpiece placed on the moldingsurface and that is on a periphery of the concave portion; and amicro-rough layer which is formed by performing a particulate coatingprocess on at least one of a portion of the pad, for pressing theworkpiece, and a portion of the molding surface, corresponding to theportion of the pad.
 2. The press molding die according to claim 1,wherein an average height of roughness of the micro-rough layer is 0.01to 0.06 mm.
 3. The press molding die according to claim 1, wherein theparticulate coating process is performed using a silicofluoric chromeplating solution.
 4. The press molding die according to claim 3, whereinthe silicofluoric chrome plating solution contains 200 to 300 g ofchromic anhydride, 1 to 8 g of sodium silicofluoride, and 0.5 to 1.5 gof sulfuric acid per liter, and the particulate coating process isperformed in a condition in which a temperature of the plating solutionis 40 to 50° C., a current density is 100 to 150 A/dm², and a platingtime is 3 to 10 minutes.
 5. The press molding die according to claim 1,wherein a plurality of grooves which are parallel to each other, andanother plurality of grooves which are parallel to each other are formedon the molding surface such that the plurality of grooves and the otherplurality of grooves extend in different directions.
 6. A manufacturingmethod of a press molding die, comprising the steps of: forming a punchwhich presses a workpiece; forming a molding die having a moldingsurface on which the workpiece is placed and a concave portion which isformed on the molding surface and which has a shape corresponding to thepunch; forming a pad which presses a portion that is a part of theworkpiece placed on the molding surface and that is on a periphery ofthe concave portion; and forming a micro-rough layer by performing aparticulate coating process on at least one of a portion of the pad, forpressing the workpiece, and a portion of the molding surface,corresponding to the portion of the pad.
 7. The manufacturing method ofa press molding die according to claim 6, wherein an average height ofroughness of the micro-rough layer is 0.01 to 0.06 mm.
 8. Themanufacturing method of a press molding die according to claim 6,wherein the particulate coating process is performed using asilicofluoric chrome plating solution.
 9. The manufacturing method of apress molding die according to claim 8, wherein the silicofluoric chromeplating solution contains 200 to 300 g of chromic anhydride, 1 to 8 g ofsodium silicofluoride, and 0.5 to 1.5 g of sulfuric acid per liter, andthe particulate coating process is performed in a condition in which atemperature of the plating solution is 40 to 50° C., a current densityis 100 to 150 A/dm², and a plating time is 3 to 10 minutes.
 10. Themanufacturing method of a press molding die according to claim 6,wherein a plurality of grooves which are parallel to each other, andanother plurality of grooves which are parallel to each other are formedon the molding surface such that the plurality of grooves and the otherplurality of grooves extend in different directions.